Casting freely oxidizable metal



Patented July 25, 1933 rennin JOHN A. GANN, OF MIDLAND, MICHICFAN, ASSIGNOR .TO THE DOW CHEMICAL COM- IPANY,

OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN CASTING FREELY O XIDIZABLE METAL No Drawing.

found adaptable for the casting of other similar readily oxidizable metals. Difficulties encountered in melting and handling, in molten state, magnesium or an alloy largely composed of this metal are well known, and those difiiculties are still present when it is attempted to introduce such metal into a mold in any process of casting. For example, when green sand castings are made in the ordinary way by simply pouring the molten magnesium or light metal alloy into an untreated sand mold, not only is there a pronounced tendcncy for the metal to burn in the sprue, but the surface of the casting formed by contact with the complementary surface of the mold tends to become oxidized, pitted, or both, due to the formation of a powder (presumably an oxide or a nitride of the metal). Where the casting poured in this manner is -of relatively heavy section, it either comnot serious enough to prevent the cast ar-' ticle from being finished when removed from the mold, the casting has an unsightly appearance and a certain loss of metal is involved. It is to be noted, of course, that the cleaner the casting, the more easily may the subsequent finishing operations be carried out. H

It has heretofore. been proposed to overcome these difiiculties, specifically in casting magnesium and alloys containing the same in dry sand molds, by dusting the mold with sulphur prior to casting the metal therein, the sulphur giving off in contact with the molten metal a vapor which is more easily oxidizable than magnesium. This Application filed July 7, 1930. Serial No. 466,080.

procedure, however, has the objection that it is obviously difficult to correctly gauge the amount of sulphurthus used and particularly if an excess is applied to the surface, either of the mold properlor the core, so much vapor may be generated that some of it becomes entrapped during the period that the metal is solidifying, the result being blow-holes or surface shrinks in the casting.

More recently it has been proposed to avoid the dificulties encountered in casting magnesium and its alloys by using a molding composition consisting of pulverized carbon, pulverized soapstone, magnesium oxide and a light bodied mineral oil. I have found, however, that the use of magnesium oxide, which is commercially sold as a fine powder, is not only unnecessary but detrimental since it makes the mold less porous and thus tends to prevent the ready escape of gases generated during casting. This in itself is undesirable since it causes pitting, surface shrinks, and general surface injury to the casting. I have further found that the use of magnesium oxide in contact with hot magnesium and its alloys accelerates or promotes the oxidation of the metal. This discovery is incorporated in; my copending Patent No. 1,871,315 wherein I have described and claimed the casting of so bound with non-aqueous liquids and consistso ing largely of pulverized or finelydivided carbon, I discovered that still better results could be obtained in the way of roducing castings of readily oxidizable meta s, such as magnesium and its alloys, by incorporating in such molding compositions an oxidation inhibitor. The inhibitors used for this purpose may be admixed directly with the molding composition or may be applied in solution or suspension form. The materials that I have found best suited for the purpose at hand are boric acid, sulphur, ammonium compounds, such as ammonium chloride and, ammonium sulphate, or mixtures ofv'these.

Accordingly, among the objects of the present invention is the production of an improved molding composition suitable for use in casting readily oxidizable metals such as magnesium and its alloys, the use of such composition further permitting the production of castings having a good surface appearance. Other objects and advantages will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, consists of the method and product hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail means and modes of carrying out the invention, such disclosed means and modes illustrating, however, but several of the various ways in which the principle of the invention may be used.

I have discovered that, where pulverized or finely divided carbon is used instead of.

sand for forming a mold, such mold has a much higher heat conductivity than a similar sand mold. This increased heat-conduc tivity causes the hot readily oxidizable metal being poured into the mold to chill prompt ly which not only decreases the period wherein rapid oxidation can take place but produces a fine grain structure in the casting which exhibits superior properties as compared with a like casting made in sand. In this connection it is to be noted that carbon is chemically and physically not an equivalent to sand since itis not an oxide; it is combustible and has a much higher heat conductivity than sand. I am aware that graphite, powdered coal,and lampblack have been used as facings and washes for molds used in the casting of iron and steel; however, the problem encountered there is in no way com arable with that encountered in the casting of an extremely readily oxidizable .metal, such as magnesium and its'alloys,

which has to be handled and poured at a temperature ,whereat it readily ignites and burns.

My improved molding composition, consisting of pulverized carbon, anon-aqueous liquid binder, specifically mineral oil, with or without a plasticizing agent and having incorporated therein an oxidation inhibitor, may be used to form a mold to produce a casting of any desired shape or size, e. g. a crank case for an internal combustion engine or like article, and such mold, if desired, may have incorporated therein cores or metal parts as is well known to the art.

If, with the carbon base molding composition used in making such mold, approximately of 1 per cent to 10 per cent of the boric acid, ammonium compounds, sulphur, or a combination of these or other like oxidation inhibitors be intermixed, a very satisfactory result in the way of a casting is obtained upon pouring the metal into the -of course that ordinarily unless the casting section is very thin an amount of the above noted agents greater than the minimum' stated should be used. For general casting service with such compositions, I have found that 3 per cent of boric acid, or 4 per cent ammonium chloride, or 4 per cent of sulphur admixed therewith will produce castings of readily oxidizable metals that are substantially free from burning and exhibit an exceptionally good surface finish. The use of my present invention is concerned broadly with the treatment of non-aqueous bound molding compositions wherein pul verized or finely divided carbon is a major constituent. As specific examples of such mixtures may be noted the pulverized carbon-oil composition wherein the proportions by weight of the ingredients vary from to 90 per cent for the carbon and 25 to 10 per cent for the oil. In like manner such pulverized carbon-oil composition may include a plasticizing agent (1 to 3p per cent) such as soapstone, or some other suitable silicate such as bentonite. Such pulverized carbon-oiLsoap'stone composition is equally applicable to treatment according to my invention as is the pulverized carbon-oil composition. While I have given percentage ranges and preferred amounts of oxidation verized carbon molding composition I do not wish to be strictly limited to those specifio ranges since I have found that as high as 20 per cent by weight of the oxidation inhibiting agent or agents can be used with satisfactory results. I have further noted that where sulphur is used according to the method described as the percentage approaches 10 the casting produced takes on a dark appearance; however, when the percentage of sulphur is increased to 20 the dark appearance almost completely disappears. Even the dark castings, however, when pickled according to common practice exhibit an exceptionally good surface, which shows that the discoloration is not detrimental to the formation of good castings. The castings made with boric acid as the protective agent normally take on a beautiful iridescent color while the ammonium chloride protected castings normally assume a grayish appearance. These castings however, when pickled or cleaned according to common practice exhibit sound castin s having an exceptionally good surface. hefollowing examples show in detail two preferred formulae for my improved molding composition.

' Example 1 Where" using pulverized carbon and oil alone with the oxidation inhibitor, I have found that very good castings can be made by using the following composition :18% medium body mineral oil, 3% of oxidation inhibitor (boric acid, ammonium chloride,

Percentage Mesh 40-100 100-200 Through 200 Eample 2 Where using a plasticizer such as. soapstone. in addition to pulverized carbon and oil, I have found that the following com- 7 position produces very satisfactory castings:13% medium body mineral oil, 10% finely powdered soapstone, 3% of oxidation inhibitor (boric acid, ammonium chloride, ammonium sulphate, sulphur, or a mixture of them), 74% carbon (pulverized coke) having the following sieve analysis.-

Percentage Mesh 33 40-100 47 100-200 20 Through 200 In using the above compositions I have found that the castings produced present a very good surface which is substantially free from oxidation, pitting and surface shrinks, and further I have found that the tensile properties, Brinell hardness, fatigue endurance-and toughness of such castings are above the average of like articles cast in sand according to current practice. In using my improved molding composition for casting, a small portion ,of the volatile liquid binder is gasified and diiven off by the hot metal poured into the mold. Likewise a small amount of the oxidation inhibitor is driven off or otherwise lost during the casting operation. .After the so poured casting has Eoled to a point where it will not ignite or rapidly oxidize when exposed to air, it can be shaken out and the molding composition reconditioned by adding thereto suflicient of the oxidation inhibitor and non-aqueous volatile liquid binder to overcome the losses and place the composition in shape for reuse, it being noted that the other ingredientsv of the composition will be substantially unafl'ected by casting conditions. The volatile liquid binder, preferably mineral oil, acts substantially the. same in making my improved molding composition green and moldable as bound. green sand .molds but without the bad effects encountered due to water or steam giving up oxygen to oxidize the metal.-

does water in the conventional water- While I have mentioned pulverized coke as the carbon material used in my improved molding composition I do not wish to be limited to that material since I have found that pulverized gas carbon, coal, and other similar hard igh carbon materials can be used in like manner. The term carbon will accordingly be understood to broadly cover this classof materials unless otherwise specified. Further, I have found that the sieve analysis of the pulverized carbon may vary considerably from that specifb cally noted in the foregoing examples, the analysis used depending upon the permeability and bond strength desired.

Other modes of applying the principle of those explained, change being made as re? gards the method and product herein dis-. closed provided the method and product stated by any of the following claims or the equivalent thereof be employed.

I therefore particularly point out and distinctly claim as my invention 1. A method of treating a non-aqueous liquid bound carbonaceous mold part 'to' eliminate excessive burning of a readily oxidizable metal such as magnesium alloys when cast in contact therewith, which my lnvention may be employed instead of and its comprises incorporating in such mold part at least one of the materials, boric acid, ammonium salt, sulphur.

2. A method of treating a non-aqueous liquid bound carbonaceous mold part to eliminate excessive burning of a readily oxidizable metal such as magnesium and its alloys when cast in contact therewith, which comprises incorporating in such mold part at least one of the materials, boric acid, ammonium chloride, sulphur.

3. A method of treating a non-aqueous liquid bound carbonaceous mold part to eliminate excessive burning of a readily oxidizable metal such as magnesium and its alloys when cast in contact therewith, which comprises incorporating in such mold part boric acid.

4. A molding composition for casting readily oxidizable metals which comprises a mixture of pulverized carbon and at least one, of the oxidation inhibitors, boric acid, ammonium salt, sulphur, and a binding agent consisting of oil. f

5. A molding composition for casting readily oxidizable metals which comprises a mixture of pulverized corbon, boric acid, and a binding agent consisting of oil.

6. A molding composition for casting readily oxidizable metals which comprises a mixture of pulverized carbon, boric acid, and a medium body mineral oil binding agent. 7 y

7. A molding composition for casting a. readily oxidizable metal such asmagnesium and its alloys, which comprisesa mixture of ulverized carbon, pulverized soapstone, at east one of the oxidation inhibitors, boric acid, ammonium salt, sulphur, and a bindin agient consisting of a medium body minera o1 10. A molding composition for casting a readily oxidizable metal such as magnesium and its alloys which consists of a mixture of pulverized carbon (74%) pulverized soapstone (10%), boric acid (3%), and a binding agent consisting of a medium body mineral oil (13%).

' JOHN A. GANN. 

